Valves equipped with pneumatically drivable actuators are widely used to control flows of gases and/or liquids in various applications, including chemical, power or other types of process plants. Such an actuator generally includes a piston, which is moveable by influence of a drive gas (often air) in a pressure chamber, with the piston being connected to the valve closure element (a ball, blade, disc, etc.) so as to cause this to open, close or become set to a predetermined position.
The term “pneumatic” here refers to actuators that are drivable by means of a gas, such as air, or a substantially inert gas, such as nitrogen.
Pneumatically drivable actuators are advantageous in comparison with electrically or hydraulically drivable actuators, since their installation and use is associated with less regulatory requirements, such as expert knowledge in electricity or hydraulics.
In connection with, e.g., maintenance of the system in which the valve is to control a flow of gas and/or liquid, it may be desirable to safely lock the valve in a predetermined position, such as open or closed, e.g., to avoid accidental closing or opening of the valve and thereby potentially ensuing hazard to operators and/or the environment.
Hence, it is known to mechanically lock the valve closure element relative to the valve body. However, such mechanical locking may require a locking device, which is arranged, e.g., between the actuator and the valve body. Such a locking device may need to be specially sized and adapted for each valve axle diameter. Moreover, the locking device may provide a mechanical play, which can reduce the accuracy in the control of the valve closure element's position.
It is also known to mechanically lock the piston in the actuator relative to the pressure chamber, as disclosed in U.S. Pat. No. 6,105,484.
There is a demand for even safer locking mechanisms.